Control means for carburetor automatic choke

ABSTRACT

A control means for a carburetor automatic choke in which the bimetal input to the choke plate pivot shaft is varied by a lost motion variable radius connection. The control means includes linkage having a pair of pivot arms interconnected by a link. One end of the link is slidably received in a radially directed slot formed in one of the arms so that lost motion movement of the link within the slot varies the effective radial length of the arm.

0 United States Patent 1 1 1 1 m e e Keenon 1 May 1, 11973 I 1 CONTROL MEANS FOR CARBURETOR 2,410,753 1 H1946 Thompson ..261 39 B AUTOMATIC CHOKE 2,533,551 12/1950 Boyce ..26l/39 B 2,854,225 9/1958 Skay ..l23/1l9 F Inventor: Timothy Keenon, Dearbom 3,l90,623 6/1965 Ball ..261/39 B Heights, Mich. 3,259,377 7 1966 Braun @161 ..261 39 B [73] Assignee: Ford Motor Company, Dearborn, Primary Miles Mich Attorney-John R. Faulkner and Roger B. Erickson [22] Filed: Dec. 28, 1970 [57] ABSTRACT 21 Appl. No.2 101,568

A control means for a carburetor automatic choke in which the bimetal input to the choke plate pivot shaft [52] [1.8. Cl. ..261/39 B is varied by a lost motion variable radius connection, [51] Int. Cl ..F02m 1/10 The control means includes linkage having a pair of [58] Field of Search ..261/39 B, 39 C, 39 A; pivot arms interconnected by a link. One end of the 123/119 F link is slidably received in a radially directed slot formed in one of the arms so that lost motion move- [56] References Ci ment of the link within the slot varies the effective radial length of the arm. UNITED STATES PATENTS 5 Claims, 8 Drawing Figures 2,074,749 3/1937 Kirby ..261/39 B 2,362,346 11/1944 Blake ..261/39 A CONTROL MEANS FOR CARBURETOR AUTOMATIC CHOKE BACKGROUND OF THE INVENTION In modern automotive engines the carburetor choke plate generally is controlled automatically in response to engine and ambient conditions. Two basic means of control are a bimetal or thermostatic spring positioned in a stream of air from the exhaust manifold and a position and its direction of movement. For a given bimetal temperature, it is preferable to have the choke plate in a more open position when it is closing or the engine is cooling than when it is open or the engine is warming. The reason for this is that when the engine has been stopped, the bimetal cools more rapidly than the remainder of the engine and carburetor, but it fol lows quite satisfactorily the heating characteristics of an operating engine.

This invention provides a means to delay the closing of the choke plate as well as to vary the moment imposed on the choke plate by the bimetal spring. In addition, this invention provides a choke plate linkage by which the length of the effective lever arm of the choke plate is variable.

SUMMARY OF THE INVENTION A control means for a carburetor automatic choke constructed in accordance with this invention includes a pair of pivotally mounted lever arms interconnected by a link. The link is pin jointed to one arm and slidably received in a generally radially directed slot formed in the other arm. The slotted arm is secured to the choke plate pivot shaft while the other arm is secured to a bimetal spring output shaft. The movement of the link end within the slot is controlled by the angle of the slotted arm and the tension or compression load being carried by the link. Movement of the link end'from a long radius position to a short radius position, or vice versa, changes the effect of the bimetal shaft torque on the choke plate position and achieves desired engine operation characteristics.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 of the drawings is a perspective view of a carburetor embodying the invention;

FIG. 2 is an exploded, elevational view of the elements of the vacuum actuated choke pulldown assembly 29;

FIG. 3 is an elevational view showing the angle of choke arm 17 and the long radius position of link 26 within slot 27 when the engine is cold and prior to ignition;

FIG. 4 is an elevational view showing the angle of the choke arm 17 and the long radius position of link 26 within slot 27 when the engine is cold and idling just following engine ignition;

FIG. 5 is an elevational view showing the angle of the choke arm 17 and the long radius position of link 26 within slot 27 when the engine is partially warmed and idling;

FIG. 6 is an elevational view showing the angle of the choke arm 17 and the short radius position of the link 26 within slot 27 when the engine is partially warmed as in FIG. 5 and following an acceleration and sustained increased velocity;

FIG. 7 is an elevational view showing the angle of the choke arm 17 and the long radius position of link 26 within slot 27 when the engine is fully warmed and at either idle or accelerated velocities; and

FIG. 8 is an elevational view showing the angle of the choke arm 17 and the long radius position of the link 26 within slot 27 when the engine is cold as in FIG. 4 but following an acceleration and sustained velocity.

DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT FIG. 1 of the drawings illustrates a two-barrel carburetor including a main body portion 1 1 and a cover portion 12. The cover includes an air horn or induction passage 13 having a choke plate 14 pivotally mounted on a shaft 16 and fitted to open and close the air horn opening. An arm 17 is secured to the end of shaft 16 and extends downwardly as shown in FIG. 3 when the choke plate 14 is fully closed.

A thermostatic device 18 including a coiled bimetal spring 19 is attached to the main body portion 1 1 of the carburetor. In response to changes in temperature, the bimetal spring imparts a torque to a shaft 21 to which is secured a second arm 22 that pivots or rotates with the shaft 21. The bimetal spring is enclosed within a compartment 23 which communicates with the exhaust I manifold (not shown) by means of a passage 24. The

compartment is exhausted by a second passage (not shown) leading to the intake manifold of the engine.

A link 26 connects arms 17 and 22. The lower end of the link is pin jointed to arm 22 while the upper end of the link is slidingly received within a generally radially directed slot 27 formed in arm 17. An opening 28 formed in the cover portion 12 permits the link to extend directly from the choke lever 17 to the bimetal lever 22.

A vacuum actuated choke pulldown assembly 29 is incorporated in the cover portion 12 and functions to partially open a fully or nearly closed choke plate 14 in response to intake manifold vacuum following initial engine ignition. The assembly includes a diaphragm type vacuum motor in which a link 31 reciprocably moves with the diaphragm 32. A spring 33, compressed between a cap 34 and the cover portion 12, urges the link 31 upwardly, opposing the opening of the choke plate. A lever 36 is pivotally mounted to the cover portion and cammingly engages another arm 37 secured to the choke shaft 16 opposite the end of arm 17. The lever 36 and arm 37 are engageable only during the first portion of choke plate opening travel.

OPERATION The choke linkage described previously functions as a particular type of lost motion connection. The movement of the link 26 within slot 27 from a long radius to a short radius, or vice versa, varies the ratio of the connected arms 17 and 22 and thus changes the effective length of the lever arm 17 through which the force from the bimetal spring 19 is transmitted.

FIG. 1 shows a carburetor incorporating the invention under conditions in which the engine is cold and not operating and the arm 17 is in its lowermost position, as further shown in FIG. 3. The link 26 is in tension from the force of the cold bimetal spring 19 and in its long radius position. Upon starting the engine and intake manifold vacuum is created which is sensed by the vacuum pulldown assembly 29. The diaphragm 32 draws the link 31 downwardly and the lever 36 engages arm 37 to cam the choke plate 14 open and place arm 17 in the position shown in FIG. 4.

As the engine continues to idle, the bimetal spring 19 is warmed by hot exhaust gases from passage 24 so that the counterclockwise torque on shaft 21 lessens permitting the pulldown device 29 which is acting against the bimetal spring 19 to urge the choke plate 16 into a more open position, in which the arm 17 assumes the position shown in FIG. 5. It may be noted that the link 26- is held in a long radius position by the friction between the link end and the slot 27.

Upon initial acceleration following partial warmup under idle conditions, the increased air flow past the choke plate 14 tends to urge it toward an even more nearly vertical or open position. This is because the portion of the choke plate 14 downstream of the shaft 16 is significantly larger in area than the upstream portion, thus the air resistance of the plate results in a torque tending to open the plate. Upon acceleration the upper end of link 26 moves to the short radius position as shown in FIG. 6, thereby reducing the effective length of the arm 17 through which the downward force of link 26 acts.

As the engine continues to warm the bimetal spring 19 expands to the point that it exerts an upward force on the link 26, which then moves upwardly within the slot 27 to resume the long radius position, as shown in FIG. 7. In this position, the choke plate 14 is fully open.

When acceleration occurs in a cold, idling vehicle the arm 17 moves from the position of FIG. 3 to that of FIG. 7 because of the opening torque placed on the choke plate 14 by air movement. The link 26 remains in the long radius position.

It is thus seen that the choking effect of a bimetal spring is desirably reduced during the latter portion of engine warmup as the link 26 assumes a short radius position. Cold engine choking is not affected. This variable lever ratio feature also permits more design flexibility in achieving both a sufficient choking function in a cold engine and a decrease in choking in a partially warmed engine for more accurate control of engin emissions.

The invention also performs an important function during restart of a partially cooled engine. When a hot engine has been stopped, the intake manifold vacuum is eliminated and no longer draws exhaust manifold heat to the bimetal spring 19. Consequently, the bimetal spring cools more rapidly than does the remainder of the engine. Without a device to delay choke plate closing, an engine restart after partial cooling creates a tendency to flood or to be overly rich with resulting undesirably high emissions. The present invention delays the closing of the choke plate 14 insofar as the end of link 26 must travel the entire length d of the slot 27 before closing movement of the plate begins. With the subject invention the choke plate position more nearly reflects the actual engine temperature than would be possible with a conventional, pin jointed connection.

Modifications and alternations may occur to those skilled in the art which are included within the scope of the following claims.

I claim:

1. A choke plate linkage for a carburetor having a choke plate pivotally mounted within an air horn passage and a source of rotary motion responsive to ambient temperatures and engine operating conditions, said linkage comprising:

a first lever arm attached to the choke plate,

a second lever arm attached to the source of rotary motion and being rotatable therewith,

a link interconnecting said lever arms,

one end of said link having a simple pivotal connection with one of said lever arms,

the other of said lever arms having a generally radially directed slot receiving the other end of said link, said other end being slidable within said slot to vary the ratio of the first and second lever arms in response to the positions of and forces acting on said lever arms,

said lever arms and said link comprising a lost-motion linkage interconnecting the choke plate and the source of rotary motion. .2. A choke plate linkage according to claim 1 and including:

said slot being formed in said first lever arm attached to said choke plate,

said link having a generally vertical disposition between said lever arms,

said first lever arm and slot being slanted downwardly from the choke plate pivot axis when the choke plate is in a fully closed position.

said first lever arm and slot being slanted upwardly from the choke plate pivot axis when the choke plate is in a fully open position.

3. A choke plate control means comprising:

a carburetor housing having an air horn passage formed therein,

a choke plate assembly comprising a plate element and a shaft element, said choke plate assembly being pivotally mounted within said passage to open and close said passage,

21 source of rotary motion responsive to ambient temperatures and engine operating conditions,

a first lever arm attached to the choke plate,

a second lever arm attached to the source of rotary motion and being rotatable therewith,

a link interconnecting said lever arms,

one end of said link having a simple pivotal connection with said first lever arm,

said second lever arm having a generally radially directed slot slidably receiving the other end of said link,

said other end being slidable within said slot to vary the ratio of the first and second lever arms in response to the positions of and forces acting on said lever arms,

said first and second lever arms and said link comprising a lost-motion linkage.

4. A choke plate control means according to claim 3 and including:

a third lever arm attached to the choke plate,

a vacuum motor having an arm movable in response to intake manifold vacuum, said vacuum motor arm being cammingly engagable with said third lever arm to partially open said choke plate from a closed position.

5. A choke plate automatic control means comprising:

a link interconnecting said lever arms,

one end of said link having a simple pivotal connection with said second lever arm,

a lost motion connection between the other end of said link and said first lever arm comprising a generally radially directed slot formed in said first lever arm slidably receiving said other end of said link,

the relative ratios of said first and second lever arms being variable in response to the position of the received end of said link within said slot,

a third lever arm attached to the choke plate,

a vacuum motor having an arm movable in response to intake manifold vacuum, said vacuum motor arm being cammingly engagable with said third lever arm to partially open said choke plate from a closed position. 

1. A choke plate linkage for a carburetor having a choke plate pivotally mounted within an air horn passage and a source of rotary motion responsive to ambient temperatures and engine operating conditions, said linkage comprising: a first lever arm attached to the choke plate, a second lever arm attached to the source of rotary motion and being rotatable therewith, a link interconnecting said lever arms, one end of said link having a simple pivotal connection with one of said lever arms, the other of said lever arms having a generally radially directed slot receiving the other end of said link, said other end being slidable within said slot to vary the ratio of the first and second lever arms in response to the positions of and forces acting on said lever arms, said lever arms and said link comprising a lost-motion linkage interconnecting the choke plate and the source of rotary motion.
 2. A choke plate linkage according to claim 1 and including: said slot being formed in said first lever arm attached to said choke plate, said link having a generally vertical disposition between said lever arms, said first lever arm and slot being slanted downwardly fRom the choke plate pivot axis when the choke plate is in a fully closed position. said first lever arm and slot being slanted upwardly from the choke plate pivot axis when the choke plate is in a fully open position.
 3. A choke plate control means comprising: a carburetor housing having an air horn passage formed therein, a choke plate assembly comprising a plate element and a shaft element, said choke plate assembly being pivotally mounted within said passage to open and close said passage, a source of rotary motion responsive to ambient temperatures and engine operating conditions, a first lever arm attached to the choke plate, a second lever arm attached to the source of rotary motion and being rotatable therewith, a link interconnecting said lever arms, one end of said link having a simple pivotal connection with said first lever arm, said second lever arm having a generally radially directed slot slidably receiving the other end of said link, said other end being slidable within said slot to vary the ratio of the first and second lever arms in response to the positions of and forces acting on said lever arms, said first and second lever arms and said link comprising a lost-motion linkage.
 4. A choke plate control means according to claim 3 and including: a third lever arm attached to the choke plate, a vacuum motor having an arm movable in response to intake manifold vacuum, said vacuum motor arm being cammingly engagable with said third lever arm to partially open said choke plate from a closed position.
 5. A choke plate automatic control means comprising: a carburetor housing having an air horn passage formed therein, a choke plate assembly comprising a plate element and a shaft element, said choke plate assembly being pivotally mounted within said passage to open and close said passage, a source of rotary motion responsive to ambient temperatures and engine operating conditions, a first lever arm attached to the choke plate, a second lever arm attached to the source of rotary motion and being rotatable therewith, a link interconnecting said lever arms, one end of said link having a simple pivotal connection with said second lever arm, a lost motion connection between the other end of said link and said first lever arm comprising a generally radially directed slot formed in said first lever arm slidably receiving said other end of said link, the relative ratios of said first and second lever arms being variable in response to the position of the received end of said link within said slot, a third lever arm attached to the choke plate, a vacuum motor having an arm movable in response to intake manifold vacuum, said vacuum motor arm being cammingly engagable with said third lever arm to partially open said choke plate from a closed position. 